1. Field of the Invention
The present invention relates to a measurement method and system. More particularly, the present invention relates to a measurement method and system for capturing both the amplitude and phase temporal profile of a transient waveform or a selected number of consecutive waveforms having bandwidths of up to about 10 THz in a single shot or in a high repetition rate mode.
2. Description of Related Art
Continuous real time recording of ultrafast optical waveforms presents significant technical challenges for conventional electronic analog-to-digital converter (ADC) technology. In general, there are two ways to record such transient waveforms: 1) increase the electrical bandwidth and sample rate, or 2) sample the waveform repetitively. In the latter method for example, ultrafast waveform events are reproduced and sampled repetitively. Samples from different reproductions are combined to reconstruct the waveform. The reproduced displayed waveform is therefore made up of many acquisitions of the signal, similar to that of an analog sampling oscilloscope. This technique does not work for single-shot signals. In the former method, the most obvious way to obtain more samples on the waveform is to increase the sample rate by using faster analog-to-digital converters. However, a typical commercially available state-of-the-art real-time oscilloscope has a resolution on the order of about a 18 ps step response (20 GHz analog bandwidth) and a 20 ps sampling period (50 Gsample/s), making such oscilloscopes undesirable for measuring certain optical waveforms, such as single-shot transient signals, when the desired resolution (step or impulse response duration referred back to the input) requires, for example, a temporal resolution from about 1 ps down to below 100 fs.
Other high-speed detection instruments based on electron streak tubes exist. Unfortunately, these instruments are fundamentally single shot, with a limited record length and slow read out and repetition rate. Such instruments also face space-charge effects which severely limit the usable dynamic range to less than 3.3 bits for 1 ps pulses.
There are also a number of ultrafast pulse measurement techniques, such as, Frequency Resolved Optical Gating (FROG), Spectral Shear Interferometry, correlation techniques, and variations on these, which work well to measure the shape of less than 100 fs pulses. However, such systems and methods have all been demonstrated as scanned systems, which requires a repetitive waveform, or in single-shot systems, which can only record with limited time-bandwidth products. In addition, in the case of single-shot FROG, or other similar systems that map the signal into space, frame capture rates are generally limited by slow readout camera technology.
It should be noted that there are also time stretching concepts related to but dissimilar from the true temporal imaging embodiments discussed herein. One such related technique does not have an input dispersion before the signal is mixed, typically electro-optically with a Mach-Zehnder modulator, with the chirped time lens signal. It has demonstrated large time magnification and fast sampling of electrical waves, but it is limited in the minimum impulse response duration by its GHz bandwidth opto-electronic time lens process and an inherent dispersion penalty which blurs the signal and produces fades in the frequency response. Likewise earlier true temporal imaging systems using electro-optic lenses to impart a frequency chirp are also limited in bandwidth, and thus temporal resolution. In contrast, the novel all optical system presented herein can have many THz of bandwidth and does not have an inherent dispersion penalty.
Accordingly, a need exists for methods and apparatus that can measure ultrafast optical waveforms with a temporal resolution from about 1 ps down to below 100 fs of impulse response width in an expedient and efficient manner. Such a system can record in a single-shot window in time with ultrafast resolution and can be performed at a high repetition rate. Such a technology, combined with one of many demultiplexing techniques, can be used to develop a continuous, greater than THz bandwidth, real time oscilloscope. The present invention is directed to such a need.